In a notable pivot away from his optimistic promises of a sweeping trade deal, President Donald Trump on Tuesday criticized Chinese leaders for reneging on handshake agreements like one to purchase more U.S. farm products.

“China is doing very badly, worst year in 27 – was supposed to start buying our agricultural product now – no signs that they are doing so. That is the problem with China, they just don’t come through,” the U.S. leader tweeted Tuesday morning. The social media post was perhaps Trump’s most dismal description of years-old trade talks with Beijing yet.

[Trump, a native New Yorker, never publicly got behind 9/11 responders bill]

For months — even as some of his top economic and trade advisers that warned Chinese officials earlier this year had abruptly backed away from the contours of an emerging deal — the president’s public message was this: His relationship with Chinese President Xi Jinping is so good that it would help foster a final agreement.

“I had a great meeting with President Xi of China yesterday, far better than expected,” Trump tweeted on June 29, the day after he met with his Chinese counterpart on the sidelines of a G20 summit in Japan. “The quality of the transaction is far more important to me than speed. I am in no hurry, but things look very good!”

Also at that time, Trump announced that he and Xi had agreed on a number of interim moves, including the restart of stalled trade talks and an American delay on imposing planned new tariffs on $300 billion of Chinese imports. What’s more, Trump said in late June that he told Xi he would allow U.S. companies to sell equipment to Huawei, the giant Chinese telecommunications company that Beijing considers one of its industrial champions, and that China had agreed to buy more U.S. farm products.

I had a great meeting with President Xi of China yesterday, far better than expected. I agreed not to increase the already existing Tariffs that we charge China while we continue to negotiate. China has agreed that, during the negotiation, they will begin purchasing large…..

— Donald J. Trump (@realDonaldTrump) June 29, 2019

Trump’s June move on Huawei was seen as a concession and incentive to Beijing to seriously reenter the trade talks. But Chinese officials quickly disputed the American president’s claim that they would begin purchasing more U.S. agricultural products.

Trump’s contention Tuesday that China is failing to live up to the alleged farm products promise marks the second time Beijing and Washington have tiffed in recent months over the issue.

A senior Chinese official, during a Jan. 31 Oval Office meeting with Trump and other top U.S. officials, surprised the American delegation by announcing his country would ramp up its buys of American soybeans. But administration officials and analysts say that has yet to happen.

[Soybean shocker: China surprises Trump administration with Oval Office announcement]

Though Trump has touted his relationship with Xi, he let his frustrations show Tuesday about the on-again-off-again trade talks — and suggested once more that officials in Beijing would prefer to delay any final pact until after the U.S. 2020 election.

“My team is negotiating with them now, but they always change the deal in the end to their benefit. They should probably wait out our Election to see if we get one of the Democrat stiffs like Sleepy Joe,” Trump wrote. “Then they could make a GREAT deal, like in past 30 years, and continue…to ripoff the USA, even bigger and better than ever before.”

China is doing very badly, worst year in 27 – was supposed to start buying our agricultural product now – no signs that they are doing so. That is the problem with China, they just don’t come through. Our Economy has become MUCH larger than the Chinese Economy is last 3 years….

— Donald J. Trump (@realDonaldTrump) July 30, 2019

..My team is negotiating with them now, but they always change the deal in the end to their benefit. They should probably wait out our Election to see if we get one of the Democrat stiffs like Sleepy Joe. Then they could make a GREAT deal, like in past 30 years, and continue

— Donald J. Trump (@realDonaldTrump) July 30, 2019

…to ripoff the USA, even bigger and better than ever before. The problem with them waiting, however, is that if & when I win, the deal that they get will be much tougher than what we are negotiating now…or no deal at all. We have all the cards, our past leaders never got it!

— Donald J. Trump (@realDonaldTrump) July 30, 2019

The GOP president singled out the former vice president on the same day a new Quinnipiac University poll showed Biden opening a commanding lead over his Democratic primary foes. That survey, conducted July 25-28 with a 3.4 percent margin of error, showed Massachusetts Sen. Elizabeth Warren as Biden’s closest competitor at 15 percent, with California Sen. Kamala Harris at 14 percent and Vermont Sen. Bernie Sanders at 11 percent.

The poll showed Biden has a big lead among women, blacks and moderate/conservative Democrats. What’s more, 54 percent of those surveyed said they would “definitely” not vote for Trump.

Still, the U.S. president had a warning for China about a potential deal in a potential second Trump term.

“The problem with them waiting, however, is that if & when I win, the deal that they get will be much tougher than what we are negotiating now…or no deal at all,” Trump wrote. “We have all the cards, our past leaders never got it!”